Generally, a silicon wafer is produced using a process of growing a silicon single crystal ingot, a slicing process for slicing the ingot into a disk-shaped wafer, and a polishing process for making a wafer surface into a mirror surface. This silicon wafer is used for making a semiconductor device. However, as crystal defects and unintended impurities according to a growth history during the growing process of a silicon single crystal, oxygen is particularly included in the silicon single crystal. This oxygen is grown into oxygen precipitates by heat applied during the semiconductor device manufacturing procedure. The oxygen precipitates show beneficial features such as reinforcing strength of the silicon wafer and acting as an internal gettering site, but also show harmful features such as causing current leakage and fails of semiconductor devices.
Thus, there is needed a wafer wherein such oxygen precipitates are substantially not present in a denuded zone to a predetermined depth from a wafer surface on which a semiconductor device is formed, but oxygen precipitates exist with predetermined concentration and distribution in a bulk region over the predetermined depth. There have been proposed the following techniques to provide a wafer in which concentration and distribution of oxygen precipitates are controlled.
First, Korean Patent Registration No. 395391 discloses a wafer having a vacancy concentration profile that has a peak concentration at a center plane (or, in a bulk region) and is substantially decreased toward a front surface of a wafer, by means of RTP (Rapid Thermal Processing) for several to several ten seconds at a temperature of 1,150° C. or above to a wafer. Also, Korean Patent Registration No. 450676 discloses a wafer having an oxygen precipitation concentration profile in a substantial M shape as shown in FIG. 1, by means of RTP for 5 to several ten seconds at 1,100 to 1,200° C. Also, Korean Patent Registration No. 531552 discloses a wafer in which a concentration of BMD (Bulk Micro-Defect) including oxygen precipitates and bulk stacking faults shows a profile as shown in FIG. 2, by means of two-stage RTP for 1 to 5 seconds and 1 to 10 seconds respectively at 1,120 to 1,180° C. and 1,200 to 1,230° C.
However, in spite of the above documents, the demands of semiconductor device manufacturers on wafers having an oxygen precipitate concentration profile of desired concentration and distribution are more increased. In particular, the above documents are based on experiments of small-diameter wafers (8 inch or less), but semiconductor device manufacturers recently tend to use large-diameter wafers such as 12-inch wafer. However, the conventional defect control method for small-diameter wafers may not be applied to large-diameter wafers as they was. That is to say, a 12-inch wafer is also manufactured through ingot growth, slicing and polishing like 6-inch or 8-inch wafers, but its defect characteristic does not always satisfy arithmetic relations proportional to the wafer size. Thus, if the defect control method proposed in the above documents is applied based on arithmetic calculations proportion to the increase of wafer diameter, desired results are seldom obtained. Further, as wafers get greater, thermal annealing conditions applied to a wafer while making a semiconductor device are changed to make the problem more difficult. That is to say, oxygen precipitates grow into predetermined concentration and distribution due to the heat applied during the semiconductor device manufacturing process. Thus, though a wafer manufacturer supplies a wafer whose initial oxygen concentration is adjusted conforming to succeeding thermal annealing conditions (namely, thermal annealing applied during making a semiconductor device) optimized to a conventional small-diameter wafer, changing thermal annealing conditions applied during the semiconductor device manufacturing process may result in completely different results.
In addition, the above documents do not closely look into the mechanism how oxygen precipitates with desired concentration and distribution are generated, but they just check the mechanism in an indirect and inaccurate way after the fact, so they have drawbacks that they may not cope with various demands desired by semiconductor device manufacturers in an easy and reproducible way.
For example, Korean Patent Registration No. 395391 and 450676 intend to control concentration of oxygen precipitates to be formed by succeeding thermal annealing applied in the semiconductor device manufacturing process by controlling vacancy concentration of atomic level that does not allow direct checking. However, the assumption that vacancy concentration distribution of atomic level is linked to concentration distribution of oxygen precipitates is not yet proved, and direct measurement of the vacancy concentration distribution is impossible. In this consideration, the concentration profile of oxygen precipitates proposed by the above documents are considered to be lack of reliability and reproducibility. In addition, the Korean Patent Registration No. 531552 intends to control a BMD concentration profile of resultants all out in an experimental way, so any change of process conditions during low temperature thermal annealing (or, cooling process) between two-stage thermal annealing processes may derive entire different results.